Conventional rotary screw compressors use intermeshing rotors to form a compression cell (often referred to as a compression chamber) between the rotating rotors, close the cell, and then reduce the cell volume through screw rotation to compress a gas. The intermeshing rotors may be a single main rotor with two gate rotors or twin, axially-aligned, helical screw rotors. Because the gas compression process occurs in a continuous sweeping motion, rotary screw compressors produce very little pulsation or surge in the output flow of compressed gas.
As described by the physical gas laws, compressing any gas produces heat, and the hotter the gas gets the less efficient the compression process. Thus, removing heat during the compression process can improve the compression efficiency. Various means of cooling the gas in a conventional gas compressor are known. One common means, known as contact cooling, is to introduce a cooling fluid into the compression process that comes into direct contact with the compressible gas and cools it by evaporative cooling. The cooling fluid may be an oil, water, or other suitable fluid, for example. The cooling fluid may provide both a cooling function and a sealing function, such that the fluid seals the internal clearances within the compressor (e.g., between the rotors and between the each rotor and the wall of the compressor's housing). Such a fluid may be injected into the inlet flow into the compressor, where it is dispersed throughout the gas being compressed. Generally, the cooling fluid must then be removed from the resulting flow of compressed gas before being used to drive tools, equipment, and machinery. In contrast, compressing a gas without introducing a coolant into the compression cell is typically referred to as “dry” compression. However, at equivalent compression ratios, dry screw compressors generally generate higher temperatures than contact-cooled screw compressors because there is no fluid cooling in the compression cell.
Gas compressors may be required to operate under a wide range of ambient conditions, including temperature at or below the freezing point of water. Contact-cooled compressors using a cooling fluid to dissipate heat generated by the compression process may be required to operate in environments that could cause the cooling fluid to freeze, causing blockages, reduced performance, and/or damage to the compressor and/or cooling system. When operating at high ambient temperatures, the cooling fluid may become increasingly hot, making it less effective at cooling the compression process. Some existing compressor systems have various shortcomings relative to cooling the compression process. Accordingly, there remains a need for further contributions in this area of technology.